1. Field of the Invention
This invention relates to a process for producing optically active .beta.-lactones useful as starting materials for polymers or pharmaceuticals, or as intermediates of liquid crystals.
2. Description of Prior Art
An optically active .beta.-lactone has been prepared by a [2+2] addition reaction conventionally between an aldehyde and a ketene. Examples of processes for producing the optically active .beta.-lactone by a [2+2] addition reaction include (1) a process in which trichloroaldehydes or trichloroketones are reacted with ketenes in the presence of a catalytic amount of quinines or quinidines (H. Wynberg et al., J. Org. Chem. Vol 50, pp. 1977 (1985)), (2) a process in which a trichloroaldehyde is reacted with a ketene in the presence of a polymeric cinchona alkaloid as a catalyst (C. E. Song et al., Tetrahedron: Asymmetry, Vol 5, pp. 1215 (1994)), (3) a process in which an aldehyde is reacted with a ketene in the presence of an optically active binaphthol/aluminum complex (Y. Tamai et al., J. Chem. Soc. Perkin Trans. 1, pp. 1549 (1994)), (4) a process in which an aldehyde is reacted with a ketene in the presence of an optically active bissulfonamide/aluminum complex (Y. Tamai et al., J. Chem. Soc. Chem. Commun., pp. 2281 (1994)) and (5) a process in which an aldehyde is reacted with a trimethylsilylketene in the presence of an optically active bissulfonamide/aluminum complex (B. W. Dymock et al., Chem. Commun., pp. 1053 (1996)).
However, in processes (1) and (2), only a specific substrate such as a trichloroaldehyde is disclosed, and in processes (3) and (4), products with a lower enantiomer excess are obtained. Moreover, in process (5) a trimethylsilylketene which is difficult to handle is used to produce .beta.-lactones.
All the foregoing processes have drawbacks such as the use of specific substrates and insufficient enantiomer excess and hence there have been a strong demand to provide a process having none of these drawbacks.